For example, a solid polymer electrolyte fuel cell employs an electrolyte membrane. The electrolyte membrane is a polymer ion exchange membrane, and interposed between an anode and a cathode to form a membrane electrode assembly (MEA). The membrane electrode assembly is sandwiched between a pair of separators to form a unit cell. In use, normally, a predetermined number of the unit cells are stacked together to form a fuel cell stack.
In the fuel cell, a fuel gas flow field is formed in a surface of one separator facing the anode for supplying a fuel gas to the anode, and an oxygen-containing gas flow field is formed in a surface of the other separator facing the cathode for supplying an oxygen-containing gas to the cathode. Further, a coolant flow field is formed between the separators for supplying a coolant along surfaces of the separators as necessary.
In the case where metal separators are used as the separators, by providing grooves as the fuel gas flow field on one surface of the metal separator facing the anode, ridges as the back side of the grooves are formed on the other surface of the metal separator. Further, by forming grooves as the oxygen-containing gas flow field on one surface of the metal separator facing the cathode, ridges as the back side of the grooves are formed on the other surface of the metal separator.
For example, a fuel cell separator disclosed in Japanese Laid-Open Patent Publication No. 08-222237 is known. According to the disclosure, in a fuel cell stack formed by stacking a plurality of fuel cells including a solid electrolyte and electrodes on both sides of the solid electrolyte, the fuel cell separator is inserted between the fuel cells. Fuel gas flow grooves for supplying a fuel gas to one of the adjacent fuel cells are formed on one surface of the fuel cell separator, and oxygen-containing gas flow grooves for supplying an oxygen-containing gas to the other of the adjacent fuel cells are formed on the other surface of the fuel cell separator.
This separator is made of metal material having good workability. Material having good electrical conductivity is coated on front and back surfaces of the separator. Further, a large number of projections are provided at suitable intervals on the front and back surfaces of the separator. In the fuel cell stack, the projections contact the cell surfaces of the fuel cells. The fuel gas flow grooves and the oxygen-containing gas flow grooves between the separator and the adjacent fuel cells are formed by spaces between the projections.